This invention relates generally to a two-system pump. More particularily, it relates to a three-gear, two-system pump wherein one of the gears is offset so as to improve the sealing characteristics of the high-pressure system without detracting significantly from the sealing characteristics of the low-pressure system.
Gear pumps are well known in the prior art. The typical gear pump comprises a housing defining a pump chamber within which two meshing gears rotate. As they rotate, fluid is drawn into the chamber at a relatively low inlet pressure, and is directed out of the chamber at a relatively high outlet pressure.
Gear pumps are useful for suppling fluid to a wide variety of machines In many machines different pressure levels of fluid are required for operating different loads. In the prior art these requirements have been met primarily through the use of seperate gear pumps, each designed for supplying fluid at a particular pressure level Alternatively, prior art gear pumps include multiple pump stages, with outputs connected between the stages for obtaining different pressure levels. These pumps have disadvantages in that they require an excessive number of pumping gears and pump control devices Thus they are costly and bulky.
These disadvantages are overcome by a three-gear, two-system pump. Such a pump is disclosed in U.S. Pat. No. 4,204,811 issued May 27, 1980. This pump comprises three gears, the center one of which meshes with the other two such that the gears form part of two pumping systems with two simultaneously rotatable pumping gear sets. Two inlet ports are provided, along with high- and low-pressure outlet ports Upon rotation the pumping gears draw fluid through the inlet ports. The low-pressure gear set discharges fluid through the low-pressure outlet port, and the high-pressure gear set discharges fluid through the high-pressure outlet port. The relatively low pressure differential between the low-pressure outlet port and its adjacent inlet port does not pose a leakage problem. However, the relatively high pressure differential between the high-pressure outlet port and its adjacent inlet port may present a significant leakage problem. Thus there remains a need in the art for a three-gear, two-system pump in which this leakage is reduced to thereby render the high-pressure system more efficient than that of similar pumps currently available.